A semiconductor physical quantity detection sensor using the inertia force includes a movable portion, a support substrate, and a beam portion that couples the movable portion to the support substrate. When a physical quantity is applied to the sensor, the inertia force caused by the physical quantity is exerted on the movable portion, and the movable portion is displaced with respect to the support substrate. With the above displacement, a capacitance value of a capacitor formed by a movable electrode integrated with the movable portion, and a fixed electrode fixed to the support substrate is changed. The physical quantity detection sensor converts the change in the capacitance value into an electric signal, and outputs the electric signal to an arithmetic circuit. The arithmetic circuit executes arithmetic processing for converting the electric signal into the physical quantity applied to the sensor.
There has been known that when a semiconductor chip that operates as the physical quantity detection sensor is formed with the use of the MEMS technology, the movable electrode and the fixed electrode are formed in the same active layer of an SOI (silicon on insulator) wafer. In the sensor of this type, when the physical quantity is applied to the sensor, and the inertia force caused by the physical quantity is exerted on the movable portion, a displacement of the movable portion is generated in a thickness direction of the support substrate.
For example, when the movable portion is displaced in a direction of separating from the support substrate, a facing area of the movable electrode and the fixed electrode is reduced. That is, the capacitance formed by the movable electrode and the fixed electrode is reduced. On the other hand, when the movable portion is displaced in a direction of approaching the support substrate, the facing area of the movable electrode and the fixed electrode is reduced. That is, the capacitance formed by the movable electrode and the fixed electrode is reduced.
That is, in the sensor in which the movable electrode and the fixed electrode are formed in the same layer, and the displacement of the movable portion is generated in the thickness direction of the support substrate, the amount of displacement of the movable portion can be detected according to an increment or decrement of the capacitance value of the capacitance formed by the movable electrode and the fixed electrode. However, whether the direction of displacement is the direction of separating from the support substrate, or the direction of approaching the support substrate, cannot be distinguished by only the increment or decrement of the capacitance formed by the movable electrode and the fixed electrode.
Under the circumstance, a technique of PTL 1 has been proposed as the background art of this technical field. This literature discloses the technique in which a compressive stress layer formed of a thermally-oxidized film, a polycrystal silicon or silicon nitride film is formed on a surface of the beam portion that couples the movable electrode to the support substrate, as a result of which the movable electrode can be warped in a direction of separating the movable electrode from the support substrate even in a state the physical quantity is not applied to the sensor. In the sensor of this type, the movable electrode is warped in the direction of separating the movable electrode from the support substrate even in the state where the physical quantity is not applied to the sensor. Therefore, the direction and amount of displacement of the movable electrode in the thickness direction of the support substrate, that is, the direction and magnitude of the applied dynamic quantity can be appropriately detected.
Also, a technique of PTL 2 has been proposed as the background art of the this technical field. This literature discloses the technique in which a protrusion is disposed on a cap portion (a protective member that prevents water or foreign matter from being mixed into the sensor) which is joined to the sensor, and the sensor movable portion is pushed by the protrusion, as a result of which the movable electrode is moved to the support substrate side even in a state where the physical quantity is not applied to the sensor. In the sensor of this type, because the movable electrode is moved in a direction of approaching the support substrate even in the state where the physical quantity is not supplied to the sensor, the direction and amount of displacement of the movable electrode in the thickness direction of the support substrate, that is, the direction and magnitude of the applied dynamic quantity can be appropriately detected.
Also, a technique of PTL 3 has been proposed as the background art of this technical field. This literature discloses the technique in which a bias voltage is applied between an active layer of an SOI wafer on which the movable electrode and the fixed electrode are formed, and the support substrate, and an electrostatic force is used even in a state in which the physical quantity is not applied to the sensor, to thereby produce different distances of the movable electrode and the fixed electrode with respect to the support substrate. In the sensor of this type, the movable electrode can be moved in the direction of approaching the support substrate even in a state where the physical quantity is not applied to the sensor. For that reason, the direction and amount of displacement of the movable electrode in the thickness direction of the support substrate, that is, the direction and magnitude of the applied dynamic quantity can be appropriately detected.